A chemical battery such as lithium-ion secondary battery is provided with a separator between a positive electrode and a negative electrode, serving for electrically insulating respective electrodes and further keeping electrolytic solution. Also, in the lithium-ion secondary battery, a microporous film mainly made of polyethylene, polypropylene and the like are currently used. However, the microporous film is easily shrunk at high temperature in general. Therefore, when internal short-circuit occurs or when a sharp projection such as nail penetrates the battery, the separator is shrunk by instantly generated short-circuit heat to extend a short-circuit portion, which may further cause a large amount of heat of reaction to facilitate abnormal overheat.
For improving safety including the above problems, it is proposed to apply an inorganic filler dispersing slurry on a surface of an electrode active material layer followed by drying to form a porous membrane layer (Patent Document 1).
The inorganic filler dispersing slurry can be prepared by mixing inorganic filler, binder, and dispersion medium of the inorganic filler. Thus-prepared inorganic filler dispersing slurry is applied on the surface of the electrode active material layer, followed by drying with hot air.    [Patent Document 1] The Japanese Unexamined Patent Publication H7-220759